Pyrethrin
|
Pyrethrin I, R = CH3
Pyrethrin II, R = CO2CH3 |
The
pyrethrins are a pair of natural
organic compounds that have potent insecticidal activity. Pyrethrin I and pyrethrin II are structurally related
esters with a
cyclopropane core. They differ by the oxidation state of one carbon. They are viscous liquids that oxidize readily to become inactivated.
The pyrethrins are contained in the seed cases of the
perennial plant pyrethrum (
Chrysanthemum cinerariaefolium), which is grown commercially to supply the
insecticide. Pyrethrins are
neurotoxins that attack the nervous systems of all
insects. When present in amounts not fatal to insects, they still appear to have an
insect repellent effect. They are harmful to
fish, but are far less toxic to
mammals and
birds than many synthetic insecticides. They are non-persistent, being
biodegradable, and also break down easily on exposure to light or oxygen. They are considered to be amongst the safest insecticides for use around food.
The chemical structure of pyrethrins is the basis for a variety of synthetic insecticides called
pyrethroids such as
permethrin and
cypermethrin.
Merck Index, Eleventh Edition,
7978.
